Characterization of an API gravity value of crude oil by ultraviolet visible spectroscopy

ABSTRACT

A system and a method for characterizing a crude oil sample from the weight and ultraviolet visible spectroscopy of the sample, including calculating and assigning a crude oil ultraviolet visible index and using the assigned index to calculate and assign an API gravity and/or to calculate and assign an aromaticity value of the sample.

RELATED APPLICATIONS

This application

is a continuation-in-part under 35 USC § 365(c) of PCT PatentApplication No. PCT/US16/12114 filed Jan. 5, 2016, which claims thebenefit of U.S. Provisional Patent Application No. 62/099,658 filed Jan.5, 2015, and

is a continuation-in-part of U.S. patent application Ser. No. 13/400,787filed Feb. 21, 2012, which claims the benefit of U.S. Provisional PatentApplication No. 61/445,217 filed Feb. 22, 2011,

the disclosures of which are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a method and process for the evaluation ofsamples of crude oil and its fractions by ultraviolet visiblespectroscopy.

BACKGROUND OF THE INVENTION

Crude oil originates from the decomposition and transformation ofaquatic, mainly marine, living organisms and/or land plants that becameburied under successive layers of mud and silt some 15-500 million yearsago. They are essentially very complex mixtures of many thousands ofdifferent hydrocarbons. Depending on the source, the oil predominantlycontains various proportions of straight and branched-chain paraffins,cycloparaffins, and naphthenic, aromatic, and polynuclear aromatichydrocarbons. These hydrocarbons can be gaseous, liquid, or solid undernormal conditions of temperature and pressure, depending on the numberand arrangement of carbon atoms in the molecules.

Crude oils vary widely in their physical and chemical properties fromone geographical region to another and from field to field. Crude oilsare usually classified into three groups according to the nature of thehydrocarbons they contain: paraffinic, naphthenic, asphaltic, and theirmixtures. The differences are due to the different proportions of thevarious molecular types and sizes. One crude oil can contain mostlyparaffins, another mostly naphthenes. Whether paraffinic or naphthenic,one can contain a large quantity of lighter hydrocarbons and be mobileor contain dissolved gases; another can consist mainly of heavierhydrocarbons and be highly viscous, with little or no dissolved gas.Crude oils can also include heteroatoms containing sulfur, nitrogen,nickel, vanadium and other elements in quantities that impact therefinery processing of the crude oil fractions. Light crude oils orcondensates can contain sulfur in concentrations as low as 0.01 W %; incontrast, heavy crude oils can contain as much as 5-6 W %. Similarly,the nitrogen content of crude oils can range from 0.001-1.0 W %.

The nature of the crude oil governs, to a certain extent, the nature ofthe products that can be manufactured from it and their suitability forspecial applications. A naphthenic crude oil will be more suitable forthe production of asphaltic bitumen, a paraffinic crude oil for wax. Anaphthenic crude oil, and even more so an aromatic one, will yieldlubricating oils with viscosities that are sensitive to temperature.However, with modern refining methods there is greater flexibility inthe use of various crude oils to produce many desired type of products.

When produced at the well, crude oil is usually accompanied by variableamounts of sweet and sour gases, as well as formation brines having hightotal dissolved solids (TDS). The crude oil is usually stabilized anddesalted soon after its production from a well.

A crude oil assay is a traditional method of determining the nature ofcrude oils for benchmarking purposes. Crude oils are subjected to trueboiling point (TBP) distillations and fractionations to providedifferent boiling point fractions. The crude oil distillations arecarried out using the American Standard Testing Association (ASTM)Method D 2892. The common fractions and their nominal boiling points aregiven in Table 1.

TABLE 1 Fraction Boiling Point, ° C. Methane −161.5  Ethane −88.6Propane −42.1 Butanes  −6.0 Light Naphtha 36-90 Mid Naphtha  90-160Heavy Naphtha 160-205 Light Gas Oil 205-260 Mid Gas Oil 260-315 HeavyGas Oil 315-370 Light Vacuum Gas Oil 370-430 Mid Vacuum Gas Oil 430-480Heavy Vacuum Gas Oil 480-565 Vacuum Residue 565+ 

The yields, composition, physical and indicative properties of thesecrude oil fractions, where applicable, are then determined during thecrude assay work-up calculations. Typical compositional and propertyinformation obtained in a crude oil assay is given in Table 2.

TABLE 2 Property Unit Property Type Fraction Yield Weight and Volume % W% Yield All API Gravity ° Physical All Viscosity Kinematic @ 38° C. °Physical Fraction boiling >250° C. Refractive Index @ 20° C. UnitlessPhysical Fraction boiling <400° C. Sulfur W % Composition All MercaptanSulfur, W % W % Composition Fraction boiling <250° C. Nickel ppmwComposition Fraction boiling >400° C. Nitrogen ppmw Composition AllFlash Point, COC ° C. Indicative All Cloud Point ° C. IndicativeFraction boiling >250° C. Pour Point, (Upper) ° C. Indicative Fractionboiling >250° C. Freezing Point ° C. Indicative Fraction boiling >250°C. Microcarbon Residue W % Indicative Fraction boiling >300° C. SmokePoint, mm mm Indicative Fraction boiling between 150-250 Octane NumberUnitless Indicative Fraction boiling <250° C. Cetane Index UnitlessIndicative Fraction boiling between 150-400 Aniline Point ° C.Indicative Fraction boiling <520° C.

Due to the number of distillation cuts and the number of analysesinvolved, the crude oil assay work-up is both costly and time consuming.

In a typical refinery, crude oil is first fractionated in theatmospheric distillation column to separate sour gas and lighthydrocarbons, including methane, ethane, propane, butanes and hydrogensulfide, naphtha (36°-180° C.), kerosene (180°-240° C.), gas oil(240°-370° C.) and atmospheric residue (>370° C.). The atmosphericresidue from the atmospheric distillation column is either used as fueloil or sent to a vacuum distillation unit, depending on theconfiguration of the refinery. The principal products obtained fromvacuum distillation are vacuum gas oil, comprising hydrocarbons boilingin the range 370°-520° C., and vacuum residue, comprising hydrocarbonsboiling above 520° C. The crude assay data help refiners to understandthe general composition of the crude oil fractions and properties sothat the fractions can be processed most efficiently and effectively inan appropriate refining unit.

In the field of organic chemistry, UV-visible spectrophotometry, whichdeals with electronic transitions within molecules, has traditionallyprovided unique information about aromatic and heteroaromatic compoundswhich absorb strongly in the UV region (200 nm-400 nm). Despite this andowing to the complex molecular nature of crude oil, UV-visible spectraof these oils are often described as featureless, poorly definedspectra.

New rapid and direct methods to help better understand crude oilcomposition and properties from the analysis of whole crude oil willsave producers, marketers, refiners and/or other crude oil userssubstantial expense, effort and time. Therefore, a need exists for animproved system and method for determining properties of crude oilfractions from different sources and classifying the crude oil fractionsbased on their boiling point characteristics and/or properties.

SUMMARY OF THE INVENTION

Systems and methods are provided for characterizing samples of crude oilbased on an index derived from the UV visible spectra and gravity. Thewavelength maxima of known aromatic compounds and components areevaluated and extracted from the UV spectra of crude oils, which can beused to formulate and assign indices for the aromatic content of thecrude oil. Properties of the oil including API gravity, sulfur content,and other selected characteristics that define the quality and nature ofthe constituent products, are assigned as a function of these indices.Importantly, this information can be obtained relatively rapidly andinexpensively from a UV-visible scan as compared to conventional assaymethods described above.

In the method and system herein, a crude oil ultraviolet visible index(which will be referred to for convenience as “CUVISI”) is calculatedand assigned. CUVISI is used as a basis for further calculations uponwhich the crude oil can be classified. API gravity and/or aromaticityare also calculated and assigned from the CUVISI. CUVISI or API gravitycan be used to characterize the sample as extra heavy gravity, heavygravity, medium gravity, light gravity, or super light gravity crudeoil. Aromaticity, which is a measure of the percentage of the aromaticcarbon atoms present in the sample, can also be used to characterize thecrude oil sample. The correlations will provide for the necessarycharacterization of the nature of crude oils withoutfractionation/distillation typically required for the crude oil assays.The method and system will enable producers, marketers and refiners tobenchmark the oil quality and valuate the oil without performing thecustomary extensive and time-consuming crude oil assays.

BRIEF DESCRIPTION OF THE DRAWING

Further advantages and features of the present invention will becomeapparent from the following detailed description of the invention whenconsidered with reference to the accompanying drawings, in which:

FIG. 1 is a graphic plot of typical ultraviolet visible spectroscopydata for a crude oil sample solution prepared as described herein;

FIG. 2 is a process flow diagram of steps carried out to characterizethe API gravity of a crude oil sample, using the system and methodherein; and

FIG. 3 is a block diagram of a component of a system for implementingthe invention, according to one embodiment.

DETAILED DESCRIPTION OF INVENTION

In the system and method herein, spectra are obtained by a suitableknown or to be developed UV-visible spectrophotometry techniquesUV-visible spectrophotometry is carried out on a sample of crude oilaccording to the method and system herein to provide unique informationabout aromatic and heteroaromatic compounds which absorb strongly in theUV region (200 nm-400 nm). Specific individual aromatic compounds andcomponents have maxima at well-defined wavelengths. Wavelength maxima ofknown aromatic compounds and components are evaluated and extracted fromthe UV spectra of crude oils. These maxima are used to formulate indicesfor the aromatic content of the crude oil. These indices can be used toassign properties to the oil, e.g., API gravity, sulfur content, andother selected characteristics that define the quality and nature of theconstituent products. According to the provided method and system, thisinformation is obtained relatively rapidly and inexpensively from aUV-visible scan as compared to the conventional assay methods.

The system and method is applicable for naturally occurring hydrocarbonsderived from crude oils, bitumens, heavy oils, shale oils and fromrefinery process units including hydrotreating, hydroprocessing, fluidcatalytic cracking, coking, and visbreaking or coal liquefaction.

FIG. 2 shows a process flowchart in a method according to one embodimentherein. Crude oil samples were prepared and analyzed by ultravioletvisible spectrophotometry between 200-500 nm, in certain embodimentsbetween 220-400 nm. In step 210, a crude oil sample is weighed.

In step 220, solutions are prepared by dissolving a sample of the crudeoil in a two-part solvent system of a paraffinic solvent having from5-20 carbon atoms and a polar solvent, e.g., at a ratio of 90:10% v/v.In certain embodiments, effective paraffinic solvents include iso-octaneIn certain embodiments, effective polar solvents includedichloromethane.

The use of a polar solvent prevents precipitation of asphaltenes fromthe crude oil sample and ensures that all solutions are translucent forthe measurement. The polar solvents are selected based on theirHildebrand solubility factors or their two-dimensional solubilityparameters. The overall Hildebrand solubility factor is a well knownmeasure of polarity and has been calculated for numerous compounds. See,for example, the Journal of Paint Technology, Vol. 39, No. 505 (February1967). The solvents can also be described by their two-dimensionalsolubility parameter. See, for example, I. A. Wiehe, “Polygon Mappingwith Two-Dimensional Solubility Parameters”, I&EC Research, 34, 661-673(1995). The complexing solubility parameter component, which describesthe hydrogen bonding and electron donor-acceptor interactions, measuresthe interaction energy that requires a specific orientation between anatom of one molecule and a second atom of a different molecule. Thefield force solubility parameter, which describes the van der Waals anddipole interactions, measures the interaction energy of the liquid thatis not destroyed by changes in the orientation of the molecules.

The UV absorbance of the crude oil solutions is determined, forinstance, in a conventional one cm quartz cell. The absorbance values ofthe samples are summed at predetermined increments (e.g., even numbers,odd number, or increments of any number) between a predetermined range,e.g., between 200-500 nm, in certain embodiments between 220-400 nm tocalculate the characterization index.

In step 230, one or more samples of crude oil in dilute solution areanalyzed by UV-visible spectrophotometry over the wavelengths 200-500nm, in certain embodiments 220-400 nm.

In step 240, the mass and spectra data are entered into a computer. Instep 250, the CUVISI is calculated.

Equation (1) shows a crude oil ultraviolet visible index, CUVISI.

$\begin{matrix}{{CUVISI} = {\sum\limits_{i = L}^{H}\;\left( {{{Absorbance}_{({{Ni} - 220})}/x}*10} \right)}} & (1)\end{matrix}$

where:

Absorbance=absorbance value of the prepared crude oil sample solution ata specific wavelength over the range L to H at intervals of N, wherebyin certain embodiments L is between about 200 nm and 220 nm and H isbetween 400 nm and 500 nm, and N is between 1 and 3, and x is the weightof the sample used, in milligrams.

In one embodiment, in step 260 the sample is then characterized asfollows:

For CUVISI≥115, the sample is extra heavy gravity crude oil;

For 100≤CUVISI<115, the sample is heavy gravity crude oil;

For 80≤CUVISI<100, the sample is medium gravity crude oil;

For 50≤CUVISI<80, the sample is light gravity crude oil; and

For CUVISI<50, the sample is super light gravity crude oil.

In another embodiment, in step 270 the API gravity of the sample isderived from the CUVISI, and the API gravity can also be used tocharacterize the sample. The API gravity value is calculated in step 280as follows:API Gravity=X1_(API)*CUVISI² +X2_(API)*CUVISI+K _(API)  (2)

where X1_(API), X2_(API) and K_(API) are constants that are developedusing linear regression techniques.

In certain embodiments, the sample can be characterized as follows:

For API Gravity≤20, the sample is extra heavy gravity crude oil;

For 20<API Gravity<27, the sample is heavy gravity crude oil;

For 27≤API Gravity<34, the sample is medium gravity crude oil;

For 34≤API Gravity<40, the sample is light gravity crude oil; and

For API Gravity≥40, the sample is super light gravity crude oil.

In another embodiment, the aromaticity of the sample can be derived fromthe CUVISI and used to further characterize the sample.Aromaticity=X1*CUVISI² +X2_(AR)*CUVISI+K _(AR)  (3)

where X1_(AR), X2_(AR) and K are constants that are developed usinglinear regression techniques.

In certain embodiments, the sample can be characterized as follows:

For Aromaticity>10, the sample is aromatic;

For Aromaticity≤10, the sample is paraffinic/naphthenic.

An exemplary block diagram of a computer system 300 by which indicativeproperty calculation modules can be implemented is shown in FIG. 3.Computer system 300 includes a processor 310, such as a centralprocessing unit, an input/output interface 320 and support circuitry330. In certain embodiments, where the computer 300 requires directhuman interaction, a display 340 and an input device 350 such as akeyboard, mouse or pointer are also provided. The display 340, inputdevice 350, processor 310, input/output interface 320 and supportcircuitry 330 are shown connected to a bus 360 which also connects to amemory unit 370. Memory 370 includes program storage memory 380 and datastorage memory 390. Note that while computer 300 is depicted with thedirect human interface components of display 340 and input device 350,programming of modules and importation and exportation of data can alsobe accomplished over the interface 320, for instance, where the computer300 is connected to a network and the programming and display operationsoccur on another associated computer, or via a detachable input device,as are well known in the art for interfacing programmable logiccontrollers.

Program storage memory 380 and data storage memory 390 can each comprisevolatile (RAM) and non-volatile (ROM) memory units and can also comprisehard disk and backup storage capacity, and both program storage memory380 and data storage memory 390 can be embodied in a single memorydevice or separated in plural memory devices. Program storage memory 380stores software program modules and associated data, and in particularstores a crude oil UV visible index (CUVISI) calculation module and anAPI gravity characterization module that performs its calculations basedupon the CUVISI. Data storage memory 390 stores data used and/orgenerated by the one or more modules of the present system, includingmass of the oil sample, UV absorbance data or portions thereof used bythe one or more modules of the present system, and calculated datagenerated by the one or more modules of the present system.

The calculated and assigned results in accordance with the systems andmethods herein are displayed, audibly outputted, printed, and/or storedto memory for use as described herein.

It is to be appreciated that the computer system 300 can be any generalor special purpose computer such as a personal computer, minicomputer,workstation, mainframe, a dedicated controller such as a programmablelogic controller, or a combination thereof. While the computer system300 is shown, for illustration purposes, as a single computer unit, thesystem can comprise a group/farm of computers which can be scaleddepending on the processing load and database size, e.g., the totalnumber of samples that are processed and results maintained on thesystem. The computer system 300 can serve as a common multi-taskingcomputer.

The computing device 300 preferably supports an operating system, forexample, stored in program storage memory 390 and executed by theprocessor 310 from volatile memory. According to the present system andmethod, the operating system contains instructions for interfacing thedevice 300 to the calculation module(s). According to an embodiment ofthe invention, the operating system contains instructions forinterfacing computer system 300 to the Internet and/or to privatenetworks.

Example

Crude oil samples were prepared and analyzed by ultraviolet visiblespectrophotometry between 220-400 nm using a Jasco V-530 double beamspectrophotometer. The samples were weighed. Solutions were prepared bydissolving a milligram-sized sample of the crude oil in a two-partsolvent system consisting of a paraffinic solvent having from 5-20carbon atoms, preferred solvent being iso-octane, and a polar solvent,dichloromethane, at a ratio of 90:10% v/v. Dilute solutions wereprepared by dissolving the oil in a two-part solvent system consistingof iso-octane (90 mL) and dichloromethane (10 mL). In a typical solutionpreparation, one drop (˜6 mg±3 mg) of crude oil from a pre-weighedsyringe is added to 100 mL of the solvent solution. The syringe isreweighed to determine the exact amount of the crude oil added. Eachcrude oil sample is analyzed at two concentration levels, e.g., 60 mg/Land 120 mg/L.

The UV absorbance of the crude oil solutions is determined in aconventional one cm quartz cell. Solutions are analyzed in 1 cm quartzcells using a Jasco V-530 double beam spectrophotometer over thewavelengths 220-400 nm. The absorbance values of the samples, normalizedto 10 mg/L, are summed every even-numbered wavelength between 220 to 400nm to calculate the characterization index.

The instrument is allowed to warm up for 30 minutes prior to analysisand is auto-zeroed without cells in both sample and reference beams. Thereference cell is filled with the solvent mixture then placed in thereference beam. Solutions of the crude oil sample solutions prepared asdescribed above are successively placed in a clean quartz sample celland the spectra are recorded against the reference solvent blank. Thespectra are recorded at a scan speed of 100 nm/min with a fast responsetime.

Table 3 is an example of a tabulation of values for the sample of Arabheavy crude oil in the wavelength range 220-400 nm. This data isdepicted in the curve of FIG. 1.

TABLE 3 Absorbances of Arab Heavy Crude Oils at Wavelength Ranging from220-400 nm at 2 nm Interval Wave Absor., Length nm 220 3.076 222 2.841224 2.778 226 2.753 228 2.735 230 2.708 232 2.663 234 2.591 236 2.486238 2.361 240 2.236 242 2.113 244 1.994 246 1.891 248 1.811 250 1.755252 1.719 254 1.698 256 1.689 258 1.688 260 1.685 262 1.673 264 1.649266 1.621 268 1.59 270 1.552 272 1.502 274 1.447 276 1.39 278 1.341 2801.297 282 1.255 284 1.218 286 1.183 288 1.15 290 1.121 292 1.096 2941.067 296 1.036 298 1.006 300 0.981 302 0.962 304 0.935 306 0.905 3080.871 310 0.839 312 0.809 314 0.783 316 0.758 318 0.735 320 0.714 3220.696 324 0.678 326 0.662 328 0.645 330 0.627 332 0.609 334 0.59 3360.57 338 0.551 340 0.532 342 0.518 344 0.502 346 0.486 348 0.472 3500.458 352 0.445 354 0.432 356 0.418 358 0.406 360 0.394 362 0.382 3640.37 366 0.359 368 0.349 370 0.34 372 0.332 374 0.323 376 0.316 3780.309 380 0.303 382 0.299 384 0.294 386 0.292 388 0.29 390 0.289 3920.288 394 0.287 396 0.283 398 0.276 400 0.268

Equation (1) shows a crude oil ultraviolet visible index, CUVISI.

$\begin{matrix}{{{CUVISI} = {\sum\limits_{i = 220}^{400}\;\left( {{{Absorbance}_{({{2i} - 220})}/x}*10} \right)}};} & (1)\end{matrix}$

where:

Absorbance=absorbance value of the prepared crude oil sample solution ata specific wavelength over the range 220 nm to 400 nm at 2 nm intervals;

x=the weight of the sample used, in mg.

The data recorded in Table 3 produces a CUVISI of 98.697. Thisclassifies this crude oil as medium gravity crude oil based on thecharacterizations above.

Exemplary constants for equations (2) and (3) are developed by linearregression, and are given as:

-   -   X1_(API)=−0.00176    -   X2_(API)=−0.00689    -   K_(API)=45.743    -   X1_(AR)=−0.0000309999    -   X2_(AR)=0.127188    -   K_(AR)=6.36006

Using these constants for the example provided in Table 3, for whichCUVISI was determined to be 98.697:

The API Gravity is calculated as:

API Gravity=−0.00176*(98.697)²−0.00689*(98.697)+45.743=27.9, which alsoidentifies it as medium crude oil.

The Aromaticity value is calculated as:

Aromaticity=−0.0000309999*(98.697)²+0.127188*(98.697)+6.36006=18.6,which identifies the sample as aromatic.

In alternate embodiments, the present invention can be implemented as acomputer program product for use with a computerized computing system.Those skilled in the art will readily appreciate that programs definingthe functions of the present invention can be written in any appropriateprogramming language and delivered to a computer in any form, includingbut not limited to: (a) information permanently stored on non-writeablestorage media (e.g., read-only memory devices such as ROMs or CD-ROMdisks); (b) information alterably stored on writeable storage media(e.g., floppy disks and hard drives); and/or (c) information conveyed toa computer through communication media, such as a local area network, atelephone network, or a public network such as the Internet. Whencarrying computer readable instructions that implement the presentinvention methods, such computer readable media represent alternateembodiments of the present invention.

As generally illustrated herein, the system embodiments can incorporatea variety of computer readable media that comprise a computer usablemedium having computer readable code means embodied therein. One skilledin the art will recognize that the software associated with the variousprocesses described can be embodied in a wide variety of computeraccessible media from which the software is loaded and activated.Pursuant to In re Beauregard, 35 USPQ2d 1383 (U.S. Pat. No. 5,710,578),the present invention contemplates and includes this type of computerreadable media within the scope of the invention. In certainembodiments, pursuant to In re Nuijten, 500 F.3d 1346 (Fed. Cir. 2007)(U.S. patent application Ser. No. 09/211,928), the scope of the presentclaims is limited to computer readable media, wherein the media is bothtangible and non-transitory.

The system and method of the present invention have been described aboveand with reference to the attached figure; however, modifications willbe apparent to those of ordinary skill in the art and the scope ofprotection for the invention is to be defined by the claims that follow.

We claim:
 1. A system for characterizing an API gravity value of an oilsample based upon ultraviolet visible spectroscopy data derived from thesample, the system comprising: a non-volatile memory device that storescalculation modules and data, the data including ultraviolet visiblespectroscopy data indicative of absorbance values over a range ofwavelengths; a processor coupled to the memory; a first calculationmodule that calculates and assigns an index value for the oil sample asa summation of the absorbance values over the range of wavelengths,divided by the weight of the sample; and a second calculation modulethat calculates and assigns the API gravity value of the oil samplebased upon the assigned index value.
 2. The system of claim 1 whereinthe ultraviolet visible spectroscopy data is obtained by ultravioletvisible spectroscopy analysis is in a wavelength range from 220-500 nm.3. The system of claim 2, wherein the ultraviolet visible spectroscopydata is obtained from an ultraviolet visible spectroscopy analysis in awavelength range from 220-400 nm.
 4. The system of claim 1, furthercomprising a third calculation module that calculates and assigns aclassification to the oil sample based upon the assigned API gravityvalue.
 5. The system of claim 1, further comprising a third calculationmodule that calculates and assigns an aromaticity value to the oilsample based upon the index value.
 6. The system of claim 1, wherein thefirst calculation module calculates and assigns the index value basedupon the ultraviolet visible spectroscopy data and a mass of the oilsample.
 7. The system of claim 6, further comprising a third calculationmodule that calculates and assigns a classification to the oil samplebased upon the assigned API gravity value.
 8. The system of claim 6,further comprising a third calculation module that calculates andassigns an aromaticity value to the oil sample based upon the indexvalue.
 9. A system for characterizing an API gravity value of an oilsample comprising: an ultraviolet visible spectrometer that outputsultraviolet visible spectroscopy data derived from the oil sample, anon-volatile memory device that stores calculation modules and data, thedata including outputted ultraviolet visible spectroscopy dataindicative of absorbance values over a range of wavelengths; a processorcoupled to the memory; a first calculation module that calculates andassigns an index value for the oil sample as a summation of theabsorbance values over the range of wavelengths, divided by the weightof the sample; and a second calculation module that calculates andassigns the API gravity value of the oil sample based upon the assignedindex value.
 10. The system of claim 9 wherein the ultraviolet visiblespectroscopy data is obtained by ultraviolet visible spectroscopyanalysis is in a wavelength range from 220-500 nm.
 11. The system ofclaim 10, wherein the ultraviolet visible spectroscopy data is obtainedfrom an ultraviolet visible spectroscopy analysis in a wavelength rangefrom 220-400 nm.
 12. The system of claim 9, further comprising a thirdcalculation module that calculates and assigns a classification to theoil sample based upon the assigned API gravity value.
 13. The system ofclaim 9, further comprising a third calculation module that calculatesand assigns an aromaticity value to the oil sample based upon the indexvalue.
 14. The system of claim 9, wherein the first calculation modulecalculates and assigns the index value based upon the ultravioletvisible spectroscopy data and a mass of the oil sample.
 15. The systemof claim 14, further comprising a third calculation module thatcalculates and assigns a classification to the oil sample based upon theassigned API gravity value.
 16. The system of claim 14, furthercomprising a third calculation module that calculates and assigns anaromaticity value to the oil sample based upon the index value.
 17. Amethod for operating a computer to characterize an API gravity value ofan oil sample based upon ultraviolet visible spectroscopy data, themethod comprising: entering into the computer ultraviolet visiblespectroscopy data indicative of absorbance values over a range ofwavelengths; calculating and assigning an index value of the oil sampleas a summation of the absorbance values over the range of wavelengths,divided by the weight of the sample; and calculating and assigning anAPI gravity value of the sample from the assigned index value.
 18. Themethod of claim 17, wherein the ultraviolet visible spectroscopy data isobtained by ultraviolet visible spectroscopy analysis is in a wavelengthrange from 220-500 nm.
 19. The method of claim 18, wherein theultraviolet visible spectroscopy data is obtained from an ultravioletvisible spectroscopy analysis in a wavelength range from 220-400 nm. 20.The method of claim 17, further comprising calculating and assigning aclassification to the oil sample from the assigned API gravity value.21. The method of claim 17, further comprising calculating and assigningan aromaticity value to the oil sample based upon the index value. 22.The method of claim 17, further comprising weighing the sample to obtaina mass, and wherein calculating and assigning the index value is basedupon the ultraviolet visible spectroscopy data and the mass of the oilsample.
 23. The method of claim 22, further comprising calculating andassigning a classification to the oil sample from the assigned APIgravity value.
 24. The method of claim 22, further comprisingcalculating and assigning an aromaticity value to the oil sample basedupon the index value.
 25. A method for operating a computer tocharacterize an API gravity value of an oil sample comprising: operatingan ultraviolet visible spectrometer that to obtain ultraviolet visiblespectroscopy data derived from the oil sample; entering into thecomputer the ultraviolet visible spectroscopy data, the data indicativeof absorbance values over a range of wavelengths; calculating andassigning an index value of the oil sample as a summation of theabsorbance values over the range of wavelengths, divided by the weightof the sample; and calculating and assigning the API gravity value ofthe sample from the assigned index value.
 26. The method of claim 25,wherein the ultraviolet visible spectroscopy data is obtained byultraviolet visible spectroscopy analysis is in a wavelength range from220-500 nm.
 27. The method of claim 26, wherein the ultraviolet visiblespectroscopy data is obtained from an ultraviolet visible spectroscopyanalysis in a wavelength range from 220-400 nm.
 28. The method of claim25, further comprising calculating and assigning a classification to theoil sample from the assigned API gravity value.
 29. The method of claim25, further comprising calculating and assigning an aromaticity value tothe oil sample based upon the index value.
 30. The method of claim 25,further comprising weighing the sample to obtain a mass, and whereincalculating and assigning the index value is based upon the ultravioletvisible spectroscopy data and the mass of the oil sample.
 31. The methodof claim 30, further comprising calculating and assigning aclassification to the oil sample from the assigned API gravity value.32. The method of claim 30, further comprising calculating and assigningan aromaticity value to the oil sample based upon the index value. 33.The method of claim 25, further comprising preparing the sample forultraviolet visible spectroscopy analysis by diluting the sample withsolvent.
 34. The method of claim 33, wherein the solvent used is amixture of paraffinic and polar solvents.
 35. The method of claim 34,wherein the paraffinic solvent contains carbon from 5-20 atoms.
 36. Themethod of claim 34, wherein the polar solvent is selected based on itsHildebrand solubility factor or by its two-dimensional solubilityparameter.
 37. The method of claim 36, wherein the polar solvent has aHildebrand solubility rating of at least
 19. 38. The method of claim 36,wherein the two-dimensional solubility factors of the polar solvent arethe complexing solubility parameter and the field force solubilityparameter.
 39. The method of claim 38, wherein the polar solvent'scomplexing solubility parameter component describes the hydrogen bondingand electron donor acceptor interactions.
 40. The method of claim 38,wherein the polar solvent's field force solubility parameter is based onthe van der Waals and dipole interactions.
 41. The method of claim 34,wherein the paraffinic-to-polar solvent ratio is 70:30 or greater. 42.The method of claim 34, wherein the paraffinic-to-polar solvent ratio is90:10 or greater.